This invention relates to implantable medical devices (IMDs) and their various components, including flat electrolytic capacitors for same coupled through lead wires to circuitry, the capacitors having stacked cathode and anode layers, and particularly electrical connections of the capacitor anode and cathode layers with the lead wires of a capacitor connector assembly.
As described in the above-referenced parent application Ser. No. 103,876, and the provisional application that it claims priority from, a wide variety of IMDs are known in the art. Of particular interest are implantable cardioverter/defibrillators (ICDs) that deliver relatively high energy cardioversion and/or defibrillation shocks to a patient""s heart when a malignant tachyarrhythmia, e.g., atrial or ventricular fibrillation, is detected. Current ICDs typically possess single or dual chamber pacing capabilities for treating specified chronic or episodic atrial and/or ventricular bradycardia and tachycardia and were referred to previously as pacemaker/cardioverter/defibrillators (PCDs). Earlier developed automatic implantable defibrillators (AIDs) did not have cardioversion or pacing capabilities. For purposes of the present invention ICDs are understood to encompass all such IMDs having at least high voltage cardioversion and/or defibrillation capabilities.
Generally speaking, it is necessary to employ a DC-DC converter within an ICD implantable pulse generator (IPG) to convert electrical energy from a low voltage, low current, electrochemical cell or battery enclosed within the IPG housing to a high voltage energy level stored in one or more high energy storage capacitor, as shown for example, in commonly assigned U.S. Pat. No. 4,548,209. The conversion is effected upon confirmation of a tachyarrhythmia by a DC-DC xe2x80x9cflybackxe2x80x9d converter which includes a transformer having a primary winding in series with the battery and a secondary winding in series with the high energy capacitor(s) and an interrupting circuit or switch in series with the primary coil and battery that is periodically opened and closed during a charging cycle. Charging of the high energy capacitor is accomplished by inducing a voltage in the primary winding of the transformer creating a magnetic field in the secondary winding when the switch is closed. The field collapses when the current in the primary winding is interrupted by opening the switch, and the collapsing field develops a current in the secondary winding which is applied to the high energy capacitor to charge it. The repeated interruption of the supply current charges the high energy capacitor to a desired level of several hundred volts over a charging time of the charge cycle. Then, the energy is rapidly discharged from the high voltage capacitor(s) through cardioversion/defibrillation electrodes coupled to the IPG through ICD leads and arranged about or in a heart chamber or vessel if the tachyarrhythmia is confirmed as continuing at the end of the charge time. The cardioversion/defibrillation shocks effected by discharge of such capacitors are typically in the range of about 25 to 40 Joules. The process of delivering cardioversion/defibrillation shocks in this way may be repeated if an earlier delivered cardioversion/defibrillation shock does not convert the tachyarrhythmia to a normal heart rhythm.
Energy, volume, thickness and mass are critical features in the design of ICD pulse generators that are coupled to the ICD leads. The battery(s) and high voltage capacitor(s) used to provide and accumulate the energy required for the cardioversion/defibrillation shocks have historically been relatively bulky and expensive. Presently, ICD IPGs typically have a volume of about 40 to about 60 cc, a thickness of about 13 mm to about 16 mm and a mass of approximately 100 grams.
It is desirable to reduce the volume, thickness and mass of such capacitors and ICD IPGs without reducing deliverable energy. Doing so is beneficial to patient comfort and minimizes complications due to erosion of tissue around the ICD IPG. Reductions in size of the capacitors may also allow for the balanced addition of volume to the battery, thereby increasing longevity of the ICD IPG, or balanced addition of new components, thereby adding functionality to the ICD IPG. It is also desirable to provide such ICD IPGs at low cost while retaining the highest level of performance. At the same time, reliability of the capacitors cannot be compromised.
Various types of flat and spiral-wound capacitors are known in the art, some examples of which are described as follows and/or may be found in the patents listed in Table 1 of the above-referenced parent patent application Ser. No. 09/103,876.
Prior art high voltage electrolytic capacitors used in ICDs have two or more anode and cathode layers (or xe2x80x9celectrodesxe2x80x9d) and operate at room or body temperature. Typically, the capacitor is formed with a capacitor case enclosing an etched aluminum foil anode, an aluminum foil or film cathode, and a Kraft paper or fabric gauze spacer or separator impregnated with a solvent based liquid electrolyte interposed therebetween. A layer of aluminum oxide that functions as a dielectric layer is formed on the etched aluminum anode, preferably during passage of electrical current through the anode. The electrolyte comprises an ion producing salt that is dissolved in a solvent and provides ionic electrical conductivity between the cathode and the aluminum oxide dielectric. The energy of the capacitor is stored in the electrostatic field generated by opposing electrical charges separated by the aluminum oxide layer disposed on the surface of the anode and is proportional to the surface area of the aluminum anode. Thus, to minimize the overall volume of the capacitor one must maximize anode surface area per unit volume without increasing the capacitor""s overall (i.e., external) dimensions. The separator material, anode and cathode layer terminals, internal packaging, electrical interconnections, and alignment features and cathode material further increase the thickness and volume of a capacitor. Consequently, these and other components in a capacitor and the desired capacitance limit the extent to which its physical dimensions may be reduced.
Some ICD IPGs employ commercial photoflash capacitors similar to those described by Troup in xe2x80x9cImplantable Cardioverters and Defibrillators,xe2x80x9d Current Problems in Cardiology Volume XIV, Number 12, December 1989, Year Book Medical Publishers, Chicago, and as described in U.S. Pat. No. 4,254,775. The electrodes or anode and cathodes are wound into anode and cathode layers separated by separator layers of the spiral. Anode layers employed in such photoflash capacitors typically comprise one or two sheets of a high purity (99.99%), porous, highly etched, anodized aluminum foil. Cathode layers in such capacitors are formed of a non-porous, highly etched aluminum foil sheet which may be somewhat less pure (99.7%) respecting aluminum content than the anode layers. The separator formed of one or more sheet or layer of Kraft paper saturated and impregnated with a solvent based liquid electrolyte is located between adjacent anode and cathode layers. The anode foil thickness and cathode foil thickness are on the order of 100 micrometers and 20 micrometers, respectively. Most commercial photoflash capacitors contain a core of separator paper intended to prevent brittle, highly etched aluminum anode foils from fracturing during winding of the anode, cathode and separator layers into a coiled configuration. The cylindrical shape and paper core of commercial photoflash capacitors limits the volumetric packaging efficiency and thickness of an ICD IPG housing made using sane.
The aluminum anodes and cathodes of aluminum electrolytic capacitors generally each have at least one tab extending beyond their perimeters to facilitate electrical connection of all (or sets of) the anode and cathode layers electrically in parallel to form one or more capacitor and to make electrical connections to the exterior of the capacitor case. Tab terminal connections for a wound electrolytic capacitor are described in U.S. Pat. No. 4,663,824 that are laser welded to feedthrough pin terminals of feedthroughs extending through the case. Wound capacitors usually contain two or more tabs joined together by crimping or riveting.
Flat electrolytic capacitors have also been disclosed in the prior art for general applications as well as for use in ICDs. More recently developed ICD IPGs employ one or more flat high voltage capacitor to overcome some of the packaging and volume disadvantages associated with cylindrical photoflash capacitors. For example, U.S. Pat. No. 5,131,388 discloses a flat capacitor having a plurality of stacked capacitor layers. Each capacitor layer contains one or more anode foil sheet forming an anode layer having an anode tab, a cathode sheet or layer having a cathode tab and a separator for separating the anode layer from the cathode layer. In the ""388 patent, the electrode stack assembly of stacked capacitor layers is encased within a non-conductive, polymer envelope that is sealed at its seams and fitted into a chamber of a conductive metal, capacitor case or into a compartment of the ICD IPG housing, and electrical connections with the capacitor anode(s) and cathode(s) are made through feedthroughs extending through the case or compartment wall. The tabs of the anode layers and the cathode layers of all of the capacitor layers of the stack are electrically connected in parallel to form a single capacitor or grouped to form a plurality of capacitors. The aluminum anode layer tabs are gathered together and electrically connected to a feedthrough pin of an anode feedthrough extending through the case or compartment wall. The aluminum cathode layer tabs are gathered together and electrically connected to a feedthrough pin of a cathode feedthrough extending through the case or compartment wall or connected to the electrically conductive capacitor case wall.
Many improvements in the design of flat aluminum electrolytic capacitors for use in ICD IPGs have been disclosed, e.g., those improvements described in xe2x80x9cHigh Energy Density Capacitors for Implantable Defibrillatorsxe2x80x9d presented by P. Lunsmann and D. MacFarlane at CARTS 96: 16th Capacitor and Resistor Technology SymposiumMar. 11-15, 1996, and at CARTS-EUROPE96: 10th European Passive Components Symposium. Oct. 7-11, 1996, pp. 35-39. Further features of flat electrolytic capacitors for use in ICD IPGs are disclosed in U.S. Pat. Nos. 4,942,501; 5,086,374; 5,146,391; 5,153,820; 5,562,801; 5,584,890; 5,628,801; and 5,748,439, all issued to MacFarlane et al.
A number of recent patents including U.S. Pat. No. 5,660,737 and U.S. Pat. Nos. 5,522,851; 5,801,917; 5,808,857; 5,814,082; 5,908,151; 5,922,215; 5,926,357; 5,930,109; 5,968,210 and 5,983,472, all assigned to the same assignee, disclose related flat electrolytic capacitor designs for use in ICDs. In several of these patents, internal alignment elements are employed as a means for controlling the relative edge spacing of the anode and cathode layers from the conductive capacitor case. In many of these patents, each anode layer and cathode layer is provided with an outwardly extending tab, and the anode and cathode tabs are electrically connected in common to a feedthrough pin and a step feature of the conductive capacitor case, respectively. The cathode tabs are gathered together against the step feature and ultrasonically welded together and to the step feature. In the ""357 patent, the anode tabs are laser welded to one end of an aluminum ribbon that is ultrasonically welded at its other end to an aluminum layer that is ultrasonically welded to the terminal pin. The feedthrough terminal pin is electrically isolated from and extends outside and away from the case to provide an anode connection pin. A cathode connection pin is attached to the case and extends outwardly therefrom. The anode and cathode connection pins are electrically connected into the DC-DC converter circuitry, but the attachment mechanism is not described in any detail.
It is highly desirable to reduce the number of manufacturing steps and the number of parts required to make reliable electrical connections between the anode tabs and the anode feedthrough terminal pin and between the cathode tabs and the capacitor case or cathode feedthrough pin to reduce costs. It is also desirable that the space within the capacitor chamber required by these parts and the electrical connections be minimized so that capacitance can be maximized.
The present invention provides various cathode connections with a case of a case negative electrolytic capacitor that provides cathode connection terminals for attachment with a connector assembly, particularly to facilitate connection of the electrolytic capacitor with circuitry of an IMD.
In one embodiment, the capacitor comprises an electrode stack assembly and electrolyte are located within the interior case chamber of a hermetically sealed capacitor case. The electrode stack assembly comprises a plurality of capacitor layers stacked in registration upon one another, each capacitor layer comprising a cathode layer having a cathode tab, an anode sub-assembly comprising at least one anode layer having an anode tab, and a separator layer located between adjacent anode and cathode layers, whereby all adjacent cathode layers and anode layers of the stack are electrically insulated from one another by a separator layer.
Anode terminal means extend through the capacitor case side wall for electrically connecting a plurality of the anode tabs to one another and providing an anode connection terminal at the exterior of the case that is electrically insulated from the case. A cathode terminal extends through or to an encapsulation area of the capacitor case side wall via a cathode terminal passageway for electrically connecting a plurality of the cathode tabs to one another and providing a cathode connection terminal at the exterior of the case. A connector assembly is electrically attached to the anode connection terminal for making electrical connection with the anode tabs and to the cathode connection terminal for making electrical connection with the cathode tabs.
In certain embodiments, the cathode terminal passageway comprises a cathode opening extending through the case wall, and the cathode terminal comprises a cathode feedthrough pin extending through the cathode opening. A cathode feedthrough internal pin end is connected to the plurality of cathode tabs, and a cathode feedthrough external pin end extends away from the case to provide the cathode connection terminal.
In one variation, the cathode opening is hermetically welded with the cathode feedthrough pin extending through it providing the cathode connection terminal extending from the case. The exposed wire end of a cathode wire of the connector assembly is cross-wire welded to the side of cathode feedthrough wire at the cathode connection terminal.
In a further variation, the cathode opening is hermetically welded with the cathode feedthrough pin extending through it either before or after trimming or grinding the cathode feedthrough exterior pin end to be relatively flush with the exterior case wall. In this embodiment, the cathode connection terminal overlies the weld area on the exterior of the case wall. The exposed wire end of the cathode wire of the connector assembly is flush welded to the exterior of the case wall at the cathode connection terminal.
In further embodiments, the cathode terminal passageway comprises a location or section of the side wall upper opening edge having a width and depth depressed below the upper opening edge and a cover edge portion. The second cathode terminal end is trapped between the upper opening edge and the cover. The exposed wire end of the cathode wire of the connector assembly is flush welded to the exterior of the case wall at a defined cathode connection terminal.
In a first variation, the cathode terminal comprises a cathode tab extension foil of conductive material having a foil length extending between a first cathode terminal end thereof coupled with the plurality of cathode tabs and a second cathode terminal end thereof extending across the side wall upper edge opening. The second cathode terminal end of the cathode tab extension foil has a foil end width equal to or less than the step width and a foil end thickness about equal to the step depth. The second cathode terminal end extends across the side wall upper opening edge and is trapped therein by the cover hermetically sealed against the side wall upper opening edge and the foil surface at the second cathode terminal end. The cathode tab extension foil may be formed in a unitary manner as an extended one of the cathode tabs of the electrode stack assembly.
In a further variation, the cathode terminal comprises an extended length of a plurality or all of the gathered cathode tabs that extend to a second cathode terminal end. The extended tabs extend from the cathode layers across the side wall upper opening edge where the second cathode terminal ends of the extended cathode tabs are stacked. The cathode tab stack are trapped between a section of the side wall upper edge opening by the cover hermetically sealed against the side wall upper opening edge and the cathode tab stack. A mating section of the cover edge may be relieved to accommodate the thickness of stacked extended cathode tabs.
The connector block is preferably formed on an encapsulation area of the case side wall of epoxy that is cured for a period of time under elevated temperature conditions while rotating the capacitor assembly. The epoxy is applied in a liquid state, and the rotation and temperature causes the epoxy to flow into gaps of and to completely cover the anode and cathode terminal means and the electrical connections with the connector assembly, to drive air bubbles to the exposed surface, and to shape the exterior surface to a uniform, repeatable configuration.